In vitro experiments will be performed using fresh human erythrocytes in which the flux of radioactive halides will be measured in order to quantitate the kinetics of the anion exchange mechanism. This carrier mechanism has recently been shown to involve reciprocating sites which react with one anion at a time. Theoretically studies on carrier models will be carried out in parallel in order to analyze the experimental results. These results will substantially increase our knowledge about the molecular mechanism of this crucial erythrocyte transport and its regulation, if any, by intracellular proteins and metabolic intermediates. Separate experiments on the incorporation of functional components of the band 3 protein, the putative transporter, into artificial planar bilayer membranes are proposed.